1. Technical Field of the Invention
The present invention relates to a method of managing chemical used for removing unburned carbon in fly ash with wet floatation.
2. Description of the Related Art
Conventionally, although fly ash generated at a coal fired power plant and the like is used for a mixing material for cement, an admixture for concrete, a raw material for an artificial lightweight aggregate and the like, since various problems will occur when much unburned carbon is contained in fly ash, it is necessary to remove the unburned carbon. Therefore, many arts have been proposed. Especially, when the fly ash is used as a mixing material for cement, it is considered to be the most economical method to reduce facility and operating costs that after decarburization treatment with wet floatation, wet ash is fed to a cement mill.
Here, as an example of a method of removing unburned carbon in fly ash that is utilized as a mixing material for cement, a method described in patent document 1 will briefly be explained with reference to FIG. 3.
After storing fly ash transported as a waste from a coal fired power plant and so on in a fly ash tank 1, the fly ash is supplied to a slurry tank 2 and mixed with water to generate slurry S1. Next, the fly ash slurry S1 in the slurry tank 2 is supplied to a surface reformer 4 through a pump 3. And, to the surface reformer 4 is supplied light oil as a hydrophobizing agent from a hydrophobizing agent tank 5 through a pump 6.
Next, in the surface reformer 4, to the slurry S1 to which hydrophobizing agent is added is added shearing force, and particles contained in the slurry S1 are crushed into micro pieces. The slurry S1 to which shearing force is added and other treatments are performed is supplied to an adjustment tank 7 from the surface reformer 4. Besides, to the adjustment tank 7 is supplied a foaming agent from a foaming agent tank 8 through a pump 9, and in the adjustment tank 7 are mixed the slurry S1 and the foaming agent to generate slurry S2.
Then, while the slurry S2 is supplied to a floatation machine 11 through a pump 10, air is supplied to the floatation machine 11 to generate bubbles in the floatation machine 11, and to the bubbles are adhered unburned carbon adsorbed to the hydrophobizing agent, and floating bubbles to which the unburned carbon are adhered are removed. With this, unburned carbon contained in the fly ash can be removed.
After that, froth F containing unburned carbon discharged from the floatation machine 11 is solid-liquid separated with a filter press 13 to recover the unburned carbon. It is possible to utilize the recovered unburned carbon as an auxiliary fuel in a cement kiln and the like. On the other hand, filtrate L1 generated by the filter press 13 is added to the adjustment tank 7 through a pump 14, or in the floatation machine 11, the filtrate L1 is reused for defoaming to cause unburned carbon to be adhered to the bubbles.
Meanwhile, tail T containing fly ash from the floatation machine 11 is solid-liquid separated with a filter press 12, and the fly ash whose unburned carbon content was made under 0.5 mass percent is used as a cement mixing material. On the other hand, filtrate L2 solid-liquid separated with a filter press 12 (hereinafter referred to as “circulating water C”) is cause to be circulated to the slurry tank 2 through a pump 15 to reduce chemical cost by reusing foaming agent remaining in the circulating water C.
Patent document 1: Japan Patent 3613347 gazette
However, in the conventional method of removing unburned carbon in fly ash described above, in order to continue stable operation of the floatation machine 11, the degree of foaming of the foaming agent in the floatation machine 11 was observed with eyes to determine an additional amount of foaming agent from the foaming agent tank 8 to the adjustment tank 7, so that management of the additional amount of foaming agent was not enough, which causes effect of reducing chemical cost not to reach an expected extent.
Further, since the management of additional amount of foaming agent was not sufficient, there was a case where the foaming agent was excessively supplied to the adjustment tank 7, and in such a case, the activity index of the fly ash lowered, and when the fly ash with a low activity index was utilized for a mixing material for cement, it might cause lowered initial strength of cement.